It is now widely accepted that the current and predicted global warming is primarily due to anthropogenic ‘greenhouse’ emissions. The development of biologically-derived and environmentally sustainable fuel such as bioethanol is recognised as an important means for reducing our reliance on fossil fuels. At present, bioethanol derived from the microbial-mediated conversion of cellulose and hemicellulose—the world's most abundant biological materials—has environmental, and anticipated economic viability.
The current approach to converting biomass to ethanol involves essentially a three step process; (1) a pre-treatment process (including acid explosion) to allow access of cellulolytic enzymes to cellulose, lignin and hemicellulose polymers, (2) enzymatic degradation of polysaccharides to sugars, and (3) the anaerobic fermentation of sugars to ethanol. Step 2, cellulose hydrolysis, is the most expensive and difficult to carry out efficiently as the often crystalline structure of cellulose requires a multi-enzyme attack to hydrolyse glycosyl residues to sugars.
One of the major components in organic waste is cellulose. Degrading cellulose can also reduce the volume of organic waste that needs to be disposed of, as well as generating useful by-products such as ethanol.
Typically, the microbial cultures used to degrade cellulose, are mesophilic with optimal operating temperatures between 25 to 45° C. There is clear evidence indicating that cellulose degradation occurs rapidly at elevated temperatures. However, to date there are only limited numbers of thermophilic cellulose degrading microorganisms and only two aerobic cellulose-degrading thermophiles. Aerobic cellulose-degrading bacteria generate substantial quantities of cellulose degrading enzymes and have high cell yields (Lynd et al., (2002) Microbial Mol Revs, 66(3): 506-577), yet only two thermophilic aerobes, Rhodothermus marinus (Halldörsdöttir et al. (1998) Appl Microbial and Biotech, 49(3): 277-284) and Caldibacillus cellulovorans (Bergquist et al. (1999) FEMS Microbial Ecol, 28(2): 99-110) are currently described. Rhodothermus marinus grows optimally at 75° C., but only has a narrow range of cellulose substrates, and notably, does not degrade crystalline cellulose (Avicel®), a highly recalcitrant cellulose. Caldibacillus cellulovorans grows optimally at 68° C. and has a wider substrate utility including Avicel®, but prefers amorphous cellulose.
There is one other reported case of an aerobic cellulolytic and thermophilic bacteria, Acidothermus cellulolyticus (Mohagheghi et al., (1986) Int. J. System. Bacteriol. 36(3):435-443). However, A. cellulyticaus has a temperature optimal of only 50-55° C. and temperature range of only 37-65° C.
A need therefore still exists for thermophilic bacteria capable of degrading cellulose, including at high temperatures. Accordingly, it is an object of this invention to provide an aerobic thermophilic bacteria capable of cellulose degradation, or to at least provide the public with a useful choice.